The present invention relates to a film advance and metering mechanism for cameras of the type used with film having a row of perforations, one for each film frame.
It has been known, for example, in U.S. Pat. Nos. 3,747,494 and 3,736,854 to stop the film transportation by sensing the perforations which are provided one for each film frame on the film. However, most of those known film metering mechanisms are so constructed that a pawl engages a film wind-up gear or ratchet gear interlocked therewith and stop the film transport operation in response to the detection of a perforation. Hence, the known mechanisms have the disadvantage that the amount of film advance varies in accordance with the speed at which the film is manually wound up. In this case, the higher the speed the greater the length of film is wound up, because it takes some time to bring the pawl into engagement with the wind-up gear after a perforation is detected and it sometimes occurs that the ratchet gear rotating at a high speed flips the pawl. Another reason for the difference in the amount of film transportation is that meshing of the pawl with the gear results in stopping a film at incrementally spaced intervals with respect to the amount of film transportation.
Further, the known mechanisms have the additional disadvantage that the film is sometimes broken by a perforation sensing member when, after the sensing member enters a perforation, film is still advanced due to improper timing between the entering of the sensing member and the meshing of the pawl. This condition may occur more frequently in the case where the top of the pawl meets a top of a gear tooth or is advanced just after the passage of the top of the tooth at the beginning of the meshing, because the film is further advanced after the entering of sensing member, i.e., commencement of the meshing, until the top of the pawl is brought into contact with the front edge of the next tooth. In those cases, even if the film is not broken, the film may be distorted and the flatness of the film at the exposure position may be spoiled.